σ-Bond initiated generation of aryl radicals from aryl diazonium salts

Abstract

Hantzsch esters and oxygen convert diazonium salts into aryl radicals, enabling rapid radical reactions to be performed in open flasks at room temperature.

Synergism between few-layer black phosphorus and graphitic carbon nitride enhances the photoredox C–H arylation under visible light irradiation

“…54 Regardless of the conventional use of transition metal-catalyst, König has introduced an alternative light-promoted C-H functionalization using organic dye molecule. 55 Following this pioneering study, C-H arylations have been reported using metal-free photocatalysts ranging from organic molecules, [56][57][58][59][60] polymers, 61 and semiconductors, namely BP, 8 g-CN/rGO, 28 biocatalyst 62 and etc. 63 Given the benefits of this new area in organic synthesis, photoredox catalysis for the direct C-H bond functionalization is now one of the best attractive options.…”

Current Advances in Meerwein-type Radical Alkene Functionalizations

“…As the attack of alkyl radicals onto arenes is, in most cases, however comparably slow, 15 an intramolecular setup is typically chosen to make this particular step more effective. 16 In the example depicted in Scheme 3 , the attack of the strongly electrophilic alkyl radical V , derived from the reaction of arenediazonium salt 5 with acryloanilines 6 , onto the attached anilide unit is followed by rearomatization to give highly substituted 2-oxindoles 7 .…”

Direct vs Indirect Grafting of Alkyl and Aryl Halides

“…[47] For example, the diazonium salt is first transformed to diazene in the presence of a Hantzsch ester, which acts as a σ-bond nucleophile and diazene is further transformed to an aryl radical in the presence of oxygen. [48] Diazonium salts containing electron-rich and sterically hindered mesityl groups enhance the reaction between aryl radicals and alkyl iodides. [47] The reaction was performed in an open vessel, at room temperature, and the products were characterized by 1 H and 13 C NMR once isolated by chromatography.…”

“…These reactions also occur in homogeneous solution by reaction of aryl radicals derived from different aryl diazonium salts and alkyl iodides [47] . For example, the diazonium salt is first transformed to diazene in the presence of a Hantzsch ester, which acts as a σ‐bond nucleophile and diazene is further transformed to an aryl radical in the presence of oxygen [48] . Diazonium salts containing electron‐rich and sterically hindered mesityl groups enhance the reaction between aryl radicals and alkyl iodides [47] .…”